16 INTRODUCTION 



inhabiting a certain piece of marsh are divided 

 into two classes, those which are pugnacious 

 and intolerant of the approach of strangers, and 

 those which welcome their presence. The nests 

 of the former will be built in isolation, those 

 of the latter in close proximity. In due course 

 eggs will be laid and incubation performed, 

 and thus far all alike will probably be successful. 

 Here, however, a critical point is reached. If 

 the young are to be freed from the risk of 

 exposure, the parents must find the necessary 

 supply of food rapidly. But manifestly all 

 will not be in a like satisfactory position to 

 accomplish this, for whereas the isolated pairs 

 will have free access to all the food in the 

 immediate vicinity of the nest, those which 

 have built in proximity to one another, meeting 

 competition in every direction, will be com- 

 pelled to roam farther afield and waste much 

 valuable time by doing so ; and under conditions 

 which can well be imagined, even this slight 

 loss of time will be sufficient to impede the 

 growth of the delicate offspring, or to lead 

 perhaps to still greater disaster. If any one 

 doubts this, let him first examine one of the 

 fragile oJffspring; let him then study the con- 

 ditions under which it is reared, observing the 

 proportion of time it passes in sleep and the 

 anxiety of the parent bird to brood ; and finally 

 let him picture to himself its plight in a wet 

 season if, in order to collect the necessary food, 

 the parents were obliged to absent themselves 

 for periods of long duration. 



